The electrical breakdown strength of a material is the magnitude of electric field required to cause the material to conduct (typically measured as the potential difference at breakdown between two electrodes in contact with opposite sides of a sample of the material, divided by the electrode separation).
Electrical permittivity {circumflex over (∈)}(ω) of a material is defined as:D0eiωt={circumflex over (∈)}(ω)E0eiωt where E0 and D0 are the amplitudes of an electric field and a corresponding displacement field in the material (respectively), ω is the angular frequency of the fields, t is time, and i is the square root of minus 1. {circumflex over (∈)}(ω) is a complex number: the real part is related to the refractive index seen by electromagnetic waves in the material; the imaginary part is related to the dielectric loss experienced by electromagnetic waves in the material. {circumflex over (∈)}(ω) is also called the frequency-dependent dielectric constant; its dc value (i.e. its value at a frequency of zero) is known as the static dielectric constant. Measuring the magnitude of the permittivity and the loss tangent (for example, by measuring the capacitance and conductance of a parallel-plate capacitor sandwiching the material being tested) enables ready calculation of the real and imaginary parts of the permittivity. The square of the magnitude of the permittivity |{circumflex over (∈)}(ω)| is of course equal to the sum of the squares of the real part {circumflex over (∈)}(ω)real and the imaginary part {circumflex over (∈)}(ω)imag of the permittivity {circumflex over (∈)}(ω), i.e. {circumflex over (∈)}(ω)real2+{circumflex over (∈)}(ω)imag2. The loss tangent is the ratio of energy dissipated to energy stored in the dielectric material. The loss tangent equals the imaginary part of the permittivity divided by the real part, i.e.
                              ɛ          ^                ⁡                  (          ω          )                    imag                                ɛ          ^                ⁡                  (          ω          )                    real        .In our experiments (described below), we measured, using an Agilent 4285A 75 kHz-30 MHz Precision LCR Meter, the magnitude of the permittivity |{circumflex over (∈)}(ω)| and the loss tangent of samples held in a sample holder similar to that shown in FIG. 4 (though not in an oil bath).
Applications exist for mechanically robust material systems that exhibit high electrical breakdown strength, and have a high dielectric constant, at frequencies ranging from a few MHz to GHz and low dielectric loss. For example, a material with a higher dielectric constant can be made into a device (for example, a lens) that is smaller than a lens with the same properties (e.g. focal length) made from a material with a lower dielectric constant. That is because the electromagnetic “path length” per unit physical length is higher in the higher-dielectric material than in the lower dielectric material; the phase of an electromagnetic wave propagating in the material progresses by a given amount over a shorter distance in the higher-dielectric material.
Most materials that are currently used for applications requiring high dielectric constants are either low-loss ceramics or liquids. Whilst both exhibit reasonable electrical performance, they are not mechanically robust, as sintered ceramics are brittle and liquid mixes can only be used in a limited range of environments and configurations. Also, many high-dielectric-constant materials exhibit high breakdown strength (BDS) when in film form (i.e. when they have thicknesses of a few microns or tens of microns) but when they are in bulk form the BDS is much reduced.
An object of the invention is to provide a dielectric material having dielectric properties similar to or better than prior-art ceramic and liquid dielectric materials and having better mechanical properties than those materials.